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In a room that is 2.44 m high, a spring (unstrained length \(=0.30 \mathrm{m}\) ) hangs from the ceiling. A board whose length is \(1.98 \mathrm{m}\) is attached to the free end of the spring. The board hangs straight down, so that its \(1.98-\mathrm{m}\) length is perpendicular to the floor. The weight of the board \((104 \mathrm{N})\) stretches the spring so that the lower end of the board just extends to, but does not touch, the floor. What is the spring constant of the spring?

Short Answer

Expert verified
The spring constant is 650 N/m.

Step by step solution

01

Understand the total extension

First, calculate how much the spring has been stretched. The ceiling is 2.44 m high, and the board is 1.98 m long, so the remaining length is the stretched length of the spring which is 0.46 m (2.44 m - 1.98 m).
02

Determine the spring's original position

The length of the spring at rest, without any force applied, is 0.30 m as given in the problem.
03

Calculate the extension of the spring

The extension of the spring is the difference between its stretched length and its original, unstrained length: 0.46 m - 0.30 m = 0.16 m.
04

Apply Hooke's Law

Hooke's Law states that the force exerted by a spring is proportional to its extension: \( F = k \times x \), where \( F \) is the force, \( k \) is the spring constant, and \( x \) is the extension. The force applied by the board is 104 N, and the extension \( x \) is 0.16 m.
05

Solve for the spring constant

Rearrange Hooke's Law to solve for the spring constant \( k \): \( k = \frac{F}{x} = \frac{104 \, N}{0.16 \, m} = 650 \, N/m \).

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Understanding the Spring Constant
The spring constant, often represented by the symbol "k," is a measure of a spring's stiffness. It tells us how much force is needed to stretch or compress a spring by a certain distance. In the context of Hooke's Law, the spring constant plays a crucial role because it directly relates force to extension with the formula: \( F = k \times x \), where \( F \) is the force applied and \( x \) represents the extension or compression of the spring.
In our scenario, the spring constant helps in determining how stiff the spring is when the board is attached to it. A larger spring constant means a stiffer spring that requires more force to extend it over the same distance. Conversely, a smaller spring constant would indicate a more flexible spring, requiring less force. Understanding this concept helps in designing systems where precise control of mechanical movement is necessary.
To find the spring constant, you would divide the force applied by the amount of extension, as demonstrated in the solution: \( k = \frac{F}{x} \).
Explaining Elasticity
Elasticity is the ability of an object or material (like a spring) to return to its original shape and size after being stretched or compressed. This concept is fundamental in understanding how materials respond to forces. A highly elastic material will return to its original form quickly after the force is removed.
In the scenario from the problem, the spring stretches to accommodate the hanging board but still holds the potential to return to its unstrained state once the board is removed. This inherent property of the spring is due to its elasticity. When a spring is deformed (stretched or compressed), it stores potential energy, which is released when the force is no longer applied.
Elasticity ensures that the spring's behavior is predictable and can be accurately calculated using Hooke's Law, making it a crucial concept in mechanics. Materials with different elasticity will behave differently when exposed to similar forces, dictating their applications in various engineering and physics-related fields.
Force and Extension Relativity
The relationship between force and extension is a foundational concept in the study of mechanics and is precisely what Hooke's Law describes. Specifically, this law states that the force needed to extend or compress a spring by some distance is linearly proportional to that distance.
This relationship is expressed as \( F = k \times x \), meaning that as the extension \( x \) increases, the force \( F \) required to maintain that extension also increases when the spring constant \( k \) is kept constant. It's important to note that this linearity holds true only within the elastic limit of the material. Beyond this limit, the spring might not return to its original shape, leading to permanent deformation or failure.
In practical terms, this means that for a given spring, doubling the force will typically double the extension, showcasing a direct proportionality as long as material limits are not exceeded. This predictable relationship is essential for engineers and physicists when designing systems requiring precise movements.
Achieving Mechanical Equilibrium
Mechanical equilibrium occurs when all forces acting on a system are balanced, resulting in no net force. This means there's no acceleration of the system, and it remains in a stable condition. Equilibrium can be static (objects at rest) or dynamic (objects moving at constant speed).
In the exercise, mechanical equilibrium is achieved when the weight of the board, acting as a downward force, is precisely balanced by the upward restoring force of the spring. The spring stretches just enough to hold the board without causing it to touch the floor.
The condition for mechanical equilibrium can be represented as:
  • The sum of forces acting on the board is zero.
  • The only forces here are the weight (gravitational force) and the spring force.

Maintaining equilibrium ensures that the system behaves predictably, with all components in balance, making systems safe and reliable in their operation. Understanding mechanical equilibrium is vital as it is a key principle in designing structures and mechanical systems that need to withstand various forces while remaining stable.

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Most popular questions from this chapter

A vertical ideal spring is mounted on the floor and has a spring constant of \(170 \mathrm{N} / \mathrm{m}\). A \(0.64-\mathrm{kg}\) block is placed on the spring in two different ways. (a) In one case, the block is placed on the spring and not released until it rests stationary on the spring in its equilibrium position. Determine the amount (magnitude only) by which the spring is compressed. (b) In a second situation, the block is released from rest immediately after being placed on the spring and falls downward until it comes to a momentary halt. Determine the amount (magnitude only) by which the spring is now compressed.

A 6.8 -kg bowling ball is attached to the end of a nylon cord with a cross- sectional area of \(3.4 \times 10^{-5} \mathrm{m}^{2} .\) The other end of the cord is fixed to the ceiling. When the bowling ball is pulled to one side and released from rest, it swings downward in a circular arc. At the instant it reaches its lowest point, the bowling ball is \(1.4 \mathrm{m}\) lower than the point from which it was released, and the cord is stretched \(2.7 \times 10^{-3} \mathrm{m}\) from its unstrained length. What is the unstrained length of the cord? (Hint: When calculating any quantity other than the strain, ignore the increase in the length of the cord.)

Two metal beams are joined together by four rivets, as the drawing indicates. Each rivet has a radius of \(5.0 \times 10^{-3} \mathrm{m}\) and is to be exposed to a shearing stress of no more than \(5.0 \times 10^{8}\) Pa. What is the maximum tension \(\overrightarrow{\mathbf{T}}\) that can be applied to each beam, assuming that each rivet carries one-fourth of the total load?

A 68.0 -kg bungee jumper is standing on a tall platform \(\left(h_{0}=\right.\) \(46.0 \mathrm{m}),\) as indicated in the figure. The bungee cord has a natural length of \(L_{0}=9.00 \mathrm{m}\) and, when stretched, behaves like an ideal spring with a spring constant of \(k=66.0 \mathrm{N} / \mathrm{m}\). The jumper falls from rest, and it is assumed that the only forces acting on him are his weight and, for the latter part of the descent, the elastic force of the bungee cord. Concepts: (i) Can we use the conservation of mechanical energy to find his speed at any point along the descent? Explain your answer. (ii) What type of energy does he have when he is standing on the platform? (iii) What types of energy does he have at point A? (iv) What types of energy does he have at point \(\mathrm{B} ?\) Calculations: What is his speed when he is at the following heights above the water: (a) \(h_{\mathrm{A}}=37.0 \mathrm{m},\) and (b) \(h_{\mathrm{B}}=15.0 \mathrm{m} ?\)

A copper rod (length \(=2.0 \mathrm{m},\) radius \(\left.=3.0 \times 10^{-3} \mathrm{m}\right)\) hangs down from the ceiling.A 9.0 -kg object is attached to the lower end of the rod. The rod acts as a "spring," and the object oscillates vertically with a small amplitude. Ignoring the rod's mass, find the frequency \(f\) of the simple harmonic motion.

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